1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having device isolation regions, and particularly to a method of forming device isolation using trenches.
2. Description of the Related Art
With micro-fabrication of a semiconductor device such as a DRAM (Dynamic Access Memory) or the like, device isolation other than device isolation carried out by conventional selective oxidation has recently been performed by an STI (Shallow Trench Isolation) technology (refer to Japanese Patent Application Laid-Open No. 2001-57382). The STI technology is intended to embed an insulating film such as an oxide film or the like in each of trenches defined in a semiconductor substrate such as silicon to thereby form a device isolation region.
However, a sufficient electrical device isolation withstand voltage was not necessarily obtained in the conventional trench device isolation. The device isolation withstand voltage depends on the shortest distance of a silicon region extending along each trench defined between adjacent devices. However, in order to make it possible to increase the distance of the silicon region, for example, the depth of each trench is made deep and the distance between the adjacent devices is made long. However, the conventional etching technology encountered difficulties in forming scaled-down trenches deeply with satisfactory control and without damage thereto and had limitations to improvements in isolation withstand voltage.
Therefore, although a technology (see Japanese Patent Application Laid-Open No. Hei 5(1993)-29283) for forming trenches different in shape as in obliquely-shaped ones, for example is also considered, it encounters a difficulty in etching or a difficulty in micro-fabrication or scale-down. Further, the application of a method of isotropically etching the bottom of each trench capacitor over its entirety to thereby widen the bottom is also considered. Since, however, an upper portion of each trench is also etched in the case of this method, it was difficult to enhance device isolation characteristics without changing a device active region.